A deck ventilator for marine use is designed to keep a compartment within a ship ventilated while preventing water from flowing into the compartment should the head of this ventilator be flooded.
Deck ventilators fall into two categories. The first category of ventilator is for use on large ships such as tankers. It comprises a tall tubular pillar mounted on the deck and carrying at its upper end, which may be many feet above deck level, a large casing containing a valve which closes automatically if a wave washes over the casing. The valve is invariably provided with a buoyant closure, such as a hollow steel ball, which is bodily displaced upwardly against a valve seat if a wave washes over the casing. As soon as the casing is again exposed, the closure drops under its own weight to a rest position to allow air to pass into and out of the compartment.
Deck ventilators of the first category are described and illustrated in U.K. Patent No. 253,696, U.S. Pat. No. 1851084 and Swedish Patent No. 7315433-8. The casing has to be large enough to accommodate a relatively large closure, as the closure must be sufficiently buoyant to exert enough thrust on the valve seat to close the ventilation. The closure must also be sufficiently heavy to cause such closure to drop vertically from its closed position a sufficient distance to allow the ventilator to be unobstructed by the closure when open. Thus it will be recognized that the first category of ventilator is a large structure and is therefore not suitable for a pleasure vessel such as a sailing yacht or motor boat.
A second category of ventilator has therefore been developed for pleasure vessels and examples of it are shown and described in British Patent No. 1502386 and P.C.T. Specification WO 82/00336. The requirements of a deck ventilator on a pleasure vessel are that it shall be unobstructive so that the external appearance of the vessel is always clean, and that it shall be sufficiently low and robust to be trodden upon and not to interfere with a proper working of a ship.
To meet the above requirements the ventilator must be squat and should have a smooth external surface. It must still be capable, however, of adequately ventilating a compartment in the vessel. The second category of ventilator is not therefore regarded as being large enough to incorporate the free-floating buoyant closure member of the first category. Instead, the ventilator is either fully open with a manual closure used to shut it in rough weather or is provided with a baffle to impede the flow of water into the ventilator and which does not severely obstruct the passage of air into and out of the ventilator. Such a baffle is shown in the British Patent. The P.C.T. specification suggests a closure which closes automatically by the weight of water entering the compartment being ventilated. While this arrangement would reduce the back flow of water though the ventilator, it does not prevent it altogether, it is dubious whether it would be regarded as a solution to the problem of how to ventilate a compartment of a pleasure vessel in a way which allows effective operation when the ventilator is open, and automatic and effective closure of the ventilator when submerged in a wave.
An object of the invention is to provide a deck ventilator for a pleasure vessel which closes automatically when under water.